This invention relates to curable organopolysiloxanes which contain oxyalkylene ether groups as well as epoxy groups to be used as curable coating agents with abhesive properties.
There is an extensive patent literature which deals with curable epoxysiloxanes and their use as coating agents. Of the large number of patents, U.S. Pat. No. 4,313,988 is named initially. In this patent, a product is described which consists of a support tape with a pressure-sensitive adhesive. On one side of the tape, a layer of a normally adhering and pressure-sensitive adhesive is provided and on the other surface, a material with abhesive properties is disposed. This material consists of a curable epoxypolysiloxane either in solution or in 100% form, which corresponds to the formula ##STR1## In this formula R represents a low molecular weight alkyl group with 1 to 3 carbon atoms;
R.sup.1 represents a monovalent hydrocarbon group with 4 to 20 carbon atoms; PA1 E is a monovalent hydrocarbon group containing epoxy groups; PA1 M is a silyl group having the formula R.sub.3 Si--; R.sub.2 R.sup.1 Si-- or R.sub.2 ESi--, R, R.sup.1 and E being as defined above; PA1 a has a value of 5 to 200; PA1 b is 0 or has a value up to 20% that of a and a+b is 5 to 200; PA1 c can assume the value 0 when M is the R.sub.2 ESi group, or is larger than 0 but smaller than 20% of the value of a+b when M is the RSi--, R.sub.2 R.sup.1 Si-- or R.sub.2 ESi-- group and PA1 n has a value of 1 to 75, PA1 M represents a terminal group having the formula A.sub.3 SiO.sub.1/2, in which A is a monovalent organic group, which is free of olefinic double bonds or hydroxyl groups and is linked directly to the silicon atom. M can also be an alkoxy group with 1 to 13 carbon atoms. PA1 D is a unit having the formula R.sub.2 SiO, in which R is a hydrocarbon group and may not contain any C.tbd.C bonds. PA1 D' is a unit having the formula RR'SiO, in which R once again is a monovalent hydrocarbon group, which may not contain any C.tbd.C groups. PA1 R' is a polyoxyalkylene unit of the formula EQU C.sub.n H.sub.2n (OC.sub.2 H.sub.4).sub.a (OC.sub.3 H.sub.6).sub.6).sub.b OR" PA1 R" is a hydrogen group, an acyl group with 1 to 8 carbon atoms or a monovalent hydrocarbon group with 1 to 13 carbon atoms, n is a whole number with an average value of 1 to 8, a and b are whole numbers, the sum of which has a value of 5 to 200 and the product a/(a+b) has a value of 1.0 to 0. PA1 D" is a unit having the formula R"'SiO, in which R is a univalent hydrocarbon group, which is free of C.tbd.C bonds. R"' is a monovalent organic group, which has at least one vicinal epoxy group. PA1 x is a whole number with an average value of 10 to 5,000; y is a whole number with an average value of 1 to x and z is a whole number with an average value of 1 to O.5x, with the proviso that the sum of y+z does not exceed 0.75.times.. PA1 R.sup.3 is a divalent alkylene group with 2 to 11 carbon atoms, PA1 z is 0 or 1, PA1 y is 0 or 1, PA1 z+y is 1 or 2, PA1 n has an average value of 2 to 3 in the average molecule, the absolute values of n being 2, 3 or 4 and PA1 x has a value of 1 to 200, PA1 R.sub.2 can be an alkyl group with 1 to 20 carbon atoms, an aryl group or an aralkyl group; examples of alkyl groups are methyl, ethyl, propyl, butyl, hexyl, decyl, dodecyl, hexadecyl or octadecyl groups; the phenyl group particularly comes into consideration as an aryl group and the benzyl group as an aralkyl group; PA1 R.sub.2 can also be an epoxy group, which is linked over an Si--C bond to the silicon atom of the polysiloxane; examples of such epoxy groups are already named in the description of the state of the art; PA1 R.sub.2 can furthermore correspond to formula I, in which R.sup.3 has the meaning given above and the subscripts n, x, y and z have the already given values; and PA1 subscript a indicates the number of chain-forming difunctional siloxy units and has a value of 1 to 1,000 and preferably of 5 to 200 and b indicates the number of trifunctional, branched siloxy units and has a value of 0 to 10 and preferably of 0 to 2. PA1 m=0.5 ##STR11## A.sup.3 = ##STR12## A.sup.4 =--O(C.sub.2 H.sub.4 O).sub.2 H m=0.7 PA1 n=0.3 ##STR13## A.sup.5 = ##STR14## A.sup.6 =--O(C.sub.2 H.sub.4 O).sub.10 --C.sub.4 H.sub.8 --O(C.sub.2 H.sub.4 O).sub.10 --H PA1 m=0.7 PA1 n=0.3 ##STR15## A.sup.1, A.sup.2 as defined for compound 1 m=0.75 PA1 n=0.25 ##STR16## A.sup.1, A.sup.2 as defined for compound 1 m=0.8 PA1 n=0.2 ##STR17## A.sup.3, A.sup.4 as defined for compound 2 m=0.8 PA1 n=0.2 PA1 R is an alkyl group with 1 to 8 carbon atoms PA1 R' is the same as R or is a monovalent, epoxy-function organic group with 2 to 20 carbon atoms, with the proviso that at least two R' groups are monovalent, epoxy-functional organic groups and x has a value of 0 to 20.
with the proviso that the monovalent hydrocarbon group E, which contains epoxy groups, contains at least one polymerizable epoxy group of the formula ##STR2##
The rest of the E group consists of carbon and hydrogen atoms and is free of acetylenic unsaturations. In addition to the oxiran ether oxygen, a carbonyl oxygen or the ##STR3## group can be present.
Also, the preparation can contain up to 98% by weight, based on epoxypolysiloxane, of an epoxysilane.
It is pointed out in the aforementioned U.S. Pat. No. 4,313,988 that, according to the state of the art, coatings with abhesive properties, that is, with release properties towards adhesives, are widely used. Dimethylpolysiloxanes provide coatings from which an adhesive tape can be pulled off with the low release force of 4 to 16 g/cm of tape width. This measure indicates the force which must be employed to pull a 1 cm wide adhesive tape from the abhesively finished surface. If, however, adhesive tapes are to be produced, for example, in roll form, and to be finished abhesively, this degree of abhesiveness is too high, since it leads to instabilities of the coiled roll. For such purposes, coatings are desired, the release forces of which, with respect to adhesive tapes, are selective and can be increased, for example to 60 to 350 g/cm and particularly to about 60 to 200 g/cm.
The epoxysiloxanes contain at least one polymerizable epoxy group of the formula ##STR4##
The following can be named as examples of such epoxy groups: ##STR5##
The epoxy groups preferably are located terminally at the hydrocarbon group.
Preferred epoxypolysiloxanes of U.S. Pat. No. 4,313,988 are those of the formula ##STR6## wherein R is a methyl group, b has a value of 0 and the E group is a .beta.-(3,4-epoxycyclohexyl)ethyl or a c-glycidoxypropyl group.
Curing of epoxypolysiloxanes or preparations which contain such epoxypolysiloxanes is accomplished by addition and in the presence of conventional epoxy curing catalysts. Examples of such catalysts are tertiary amines, Lewis acids, such as BF.sub.3, and their complexes, such as those with ethers or amines, and polyaromatic iodonium and sulfonium complex salts, which contain SbF.sub.6.sup.- or BF.sub.4.sup.- anions as anions. Organic acids and their salts or derivatives can also be used as curing agents, such as perfluorinated sulfonic acids.
Suitable curing agents are also described in U.S. Pat. Nos. 4,394,403 and 4,310,469.
Very frequently, however, when adding the curing agent, it is observed that, depending on the structure of the preparation and particularly of the siloxanes, the miscibility and solubility of the photoinitiators (curing agents) are limited. Epoxy-functional siloxanes have already been modified in order to improve their compatibility with onium salt photoinitiators. For Example, in EP-A-O 334 068, epoxy-functional siloxanes are described, a portion of the epoxy groups of which was esterified by reaction with aromatic acids, such as benzoic acid, or unsaturated acids, such as acrylic acid. By these means, the compatibility of the epoxysiloxanes with the curing catalysts was increased. At the same time, however, the content of curable epoxy groups was decreased. Epoxy groups are reactive groups which can be activated to polymerize by weaker acids. This makes it exceedingly difficult to control the reaction. In the extreme case, the reaction can become uncontrolled and lead to gelling. Moreover, residual acid contents must be eliminated in order to ensure a long shelf life.
From EP-A-O 343 304, a polishing cloth and wiper is known which contains a wetting agent, which confers permanent hydrophilicity on the cloth. Such a wetting agent can be an organosilicon compound of the formula MD.sub.x D'.sub.y D".sub.z M.
In this formula:
wherein
The modified silicones which are described in EP-A-O 343 304 are used as hydrophilic wetting agents. Their usefulness for the preparation of curable coating compositions with abhesive properties cannot be inferred from this publication.